Streptococcus pneumoniae is a leading cause of invasive infections including pneumonia, meningitis, and sepsis, as well as non-invasive infections including pharyngitis and otitis media, and the polysaccharide capsule, a key virulence factor, is the target of current vaccines1-3. Vaccination has substantially reduced morbidity and mortality3, but has had limited impact on infection of the mucous membrane covering the eye and lining the eyelids, conjunctivitis4.
We recently collected 271 S. pneumoniae isolates during the course of clinical trials for the treatment of bacterial conjunctivitis5-7, and found that over 90% were unencapsulated8, and hence unaffected by current vaccine design. Unencapsulated S. pneumoniae strains have caused large conjunctivitis outbreaks in schools and colleges9-13, military training facilities in the US14, and other locations worldwide15. Recent outbreaks have involved one multilocus sequence type (MLST) in particular, ST44813. However, a previous study of epidemiologically unrelated conjunctivitis cases found that most cases were caused by encapsulated strains4. That study examined isolates prior to the widespread use of the PCV7 vaccine introduced in 20004.